1. Field of the Invention
The present invention relates to an optical disk system, and more particularly, to a servomechanism used in the optical disk system for causing a laser beam to trace a signal track on a optical disk.
2. Description of Related Art
Conventional optical disk players have been such that a signal track on an optical disk is scanned by a laser spot. The spot is held in focus and on a recorded track by various servomechanisms using optical sensing and electromechanical actuation. Further, such optical disk players are adapted to detect dust particles and scratches on the optical disk on the basis of a signal read out from the disk by the laser beam. The servo system is switched off, when the particles and scratches are found, in order to prevent a malfunction of the servo system which would otherwise be caused by the particles and scratches on the disk.
The above mentioned conventional optical disk players have complicated circuits since they have to include a circuit for detecting the particles and scratches on the optical disk. In addition, the conventional players have not been completely free from detection errors such as an oversight of the dust particle and scratches and a misdetection of the particles and scratches. Further, as mentioned above, when the particles and scratches are found, the servo system is switched off. Thereafter, if either the particle or the scratch are not found, the servo system is switched back on. Then, the servo system operation has been greatly disturbed as it responds to the momentary switching off of the servo system. As a result, the signal track of the disk cannot be often traced.